Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$109.57	12.570%	$123.3429	$123.34	$123.35	$123.30
Purchase #2	$249.50	12.200%	$279.939	$279.94	$279.95	$279.90
Purchase #3	$107.89	6.113%	$114.4853	$114.49	$114.50	$114.50
Purchase #4	$51.40	12.508%	$57.8291	$57.83	$57.85	$57.80
Purchase #5	$129.38	6.344%	$137.5879	$137.59	$137.60	$137.60
Purchase #6	$5.67	7.395%	$6.0893	$6.09	$6.10	$6.10
Purchase #7	$166.65	9.304%	$182.1551	$182.16	$182.15	$182.20
7 purchase totals =	$820.06		$901.4286	$901.44	$901.50	$901.40